Stanislaus-Tuolumne Experimental Forest

The Stanislaus-Tuolumne Experimental Forest covers 690 ha in the central Sierra Nevada, near Pinecrest, California. It was selected as typical of mixed conifer stands of the Sierra Nevada, specifically, those of high site-quality on mid-elevation west slopes. The Stanislaus-Tuolumne was formally created in December of 1943, though research in the area had been ongoing since the 1920’s. The effort to create the Stanislaus-Tuolumne was driven by Duncan Dunning, who had been pushing for formal designation of an experimental forest on the Stanislaus National Forest since the early 1930's. The forest consists of two tracts: the 156 ha Stanislaus Tract on the South Fork of the Stanislaus River and the 534 ha Tuolumne Tract on the lower slopes of Dodge Ridge, just south of the North Fork of the Tuolumne River. Elevations range from 1,590 to 1,950 m.

Tuolumne tract of the Stanislaus-Tuolumne Experimental forest in the foreground, with Pinecrest Lake in the background. Photo: Tom Iraci

Climate

The climate is characterized by warm dry summers and cold wet winters. Annual precipitation averages 940 mm, more than half falling as snow between December 1 and March 31. In exceptional winters, snow may accumulate to depths over 3 m. Some drifts persist until mid-May. Little precipitation falls from June through September. Air temperatures during the year usually range from -23 to 35 °C. Average monthly minimum and maximum air temperatures range from -7 to 7 °C for January to 6 to 27 °C for July. The growing season lasts about 112 days.

Soils

Moderately deep, sandy to fine sandy loam soils of the Holland series are widespread. Soils are residual, derived from granite or diorite. Shallow soils from lava caps are found on some higher slopes and ridges, but overall site quality is high.

Long-Term Data Bases

Climatological measurements on the Stanislaus-Tuolumne include air and soil temperatures, relative humidity, barometric pressure, wind velocity, cloudiness, precipitation and soil moisture. Beginning in 1932 and 1933, records were kept for 30 years at one site, 19 years at another, and 11 years at three other sites. Trees in the Tuolumne Tract have been inventoried by stand condition classes within 1-ha divisions. The Stanislaus National Forest has mapped the soils to the family level. This soil survey supersedes a more detailed survey conducted by the University of California-Berkeley in 1942.

Research, Past and Present

Early research focused on the development of harvesting methods for (old-growth stands) that would provide for regeneration of sugar pine, Jeffrey pine, and ponderosa pine. Cone and seed production of pine and fir trees were monitored for 28 years. These data were used in the definitive work on seed and cone production. Later, the "unit area control" procedure was tested at the forest. "Site factor" stations were established in the early 1930s to monitor conditions related to seedling establishment. Studies of dwarf mistletoe were conducted here in the 1960s.

In 2006 research activity on the Experimental Forest again increased with the discovery of data associated with several historic “Methods of Cutting” plots. In 1929, all trees had been mapped and understory vegetation was quantified in three approximately 4 ha plots. The plots were then logged using different methods. Leave trees were individually tagged – many of these tags remain today. All trees were remapped in 2007 and 2008, making the plots among the oldest in the USFS system. A “variable density thinning” study, comparing thinning to a variable spatial structure (with tree groups and gaps, similar to the historic stand structure), thinning to an even crown spacing, and an un-thinned control, all with or without prescribed fire, was initiated on 240 acres in 2009. Another study comparing different thinning and prescribed fire treatments for alleviating mortality of large pines was installed on 135 acres in 2009.

Collaborators

Staff members of the Summit Ranger District, Stanislaus National Forest, have and continue to work with scientists at the USDA Forest Service's Pacific Southwest (PSW) Research Station on questions of mutual interest. PSW scientists are also collaborating with faculty at University of California Berkeley and University of California Merced on several new research projects.

Research Opportunities

The Stainslaus-Tuolumne is the site of studies related to mixed conifer stands, though on a small scale, because the area is limited. The stands here are remarkable because of the component of large sugar pine trees found throughout much of the forest.

Facilities

The Stanislaus-Tuolumne's two tracts are located 51 km east of Sonora, Tuolumne County. The forest can be reached via State Route 108, an all-weather road. The road network within the forest is unpaved except for Old Strawberry Road and Crabtree Road. Only the Old Strawberry Road and the small section of State Route 108 that crosses a corner of the Stanislaus tract are maintained during the winter. There are no facilities maintained by PSW as all buildings were transferred to the Summit Ranger District in the mid-1960s.